Grade of Service and Blocking Probability

Grade of Service (GOS) is the ratio of lost traffic to offered traffic. Offered traffic is the product of the average number of calls generated by users and the average holding time per call. The actual traffic carried by the network is called the carried traffic. Accordingly, GOS is given by,

GOS=(A-A₀)/A

Where,

    A= offered traffic

    A₀= carried traffic

    A-A₀= lost traffic

So, the smaller the value of grade of service, the better is the service. 

GOS is called call congestion or loss probability and the blocking probability is called time congestion. 

Delay probability is the probability that a call experiences delay. If the offered load or the input rate of traffic far exceeds the network capacity, then the queue lengths become very large and the calls experience undesirably long delays.

Subscriber viewpoint:

        GOS = Call congestion = loss probability 

Network viewpoint:

        Blocking probability = time congestion